Field of the Invention and Related Art Statement
The present invention relates to a method of manufacturing a laminated core such as magnetic core and electric motor core, in which a number of thin core sheets made of silicon steel such as permalloy and amorphous and having a thickness smaller than 0.1 mm are stacked one on another to obtain a stacked body of core sheets and then the core sheets of the stacked body are coupled with one another.
In case of manufacturing such a laminated core, it has been known to connect thin core sheets of a stacked body with the aid of a laser beam welding. In a known welding method using the laser beam, a laser beam is continuously projected onto an outer surface of the stacked body of core sheets, so that a welding is effected continuously. It has been known that when the core sheets are coupled with one another such that a continuously welded area is formed on the outer surface of the stacked body, the influence of heat upon portions surroundings the welded area becomes large and the efficiency of a magnetic circuit including the laminated core thus formed is reduced due to the increase in the magnetic resistance, hysteresis loss and iron loss owing to the eddy current. In order to mitigate such a drawback, in Japanese Patent Publication No. 62-14087, it has been proposed another known method of manufacturing the laminated core. In this known method, the laser beam is projected intermittently on the outer surface of the stacked body of core sheets selectively at boundaries of successive core sheets. This method is effective only when the core sheets have a sufficiently large thickness as compared with a size of a laser beam spot on the stacked body, but could not be effectively applied to the manufacture of a laminated core such as a magnetic core in which silicon steel sheets or plates having a very small thickness are stacked one on another. For instance, the silicon steel plates made of permalloy for use in the magnetic core have the thickness smaller than 0.1 mm and the amorphous silicon steel sheets have the thickness usually smaller than 0.03 mm. Therefore, even if the laser beam spot is made incident upon the boundaries of successive core sheets having a very small thickness, successive welded areas are coupled with one another, and thus it is practically impossible to obtain the discontinuously welded areas.
Theoretically it is possible to obtain a fine laser beam spot by using a lens, but in practice, the laser beam is projected upon the stacked body of core sheets by means of an optical fiber, so that the size of the laser beam spot is limited by the diameter of the optical fiber and could not be made smaller than 0.2 mm. In this manner, in the known method of manufacturing the laminated core, when the thickness of the core sheets is very small, it is difficult to obtain the discrete welded areas even if the laser beam is projected onto the stacked body of core sheets intermittently.
Furthermore, in the known method, in order to separate blocks having any desired length, it is necessary to reduce the diameter of the laser beam spot smaller than a twice of the thickness of the core sheets. This results in that the known method could not be effectively applied to the laminated core such as the magnetic core formed by very thin core sheets.